Tracking the QUIC Spin Bit on Tofino

TL;DR

This paper demonstrates that P4-programmable hardware like Intel Tofino can effectively track the QUIC spin bit at line-rate, enabling passive RTT measurement while addressing hardware limitations and measurement accuracy challenges.

Contribution

It shows that core spin bit tracking can be implemented on P4 hardware with high accuracy, and discusses handling measurement issues like reordering and RTT classification.

Findings

Hardware tracking achieves near software accuracy

Protection against faulty measurements is feasible

Challenges remain with QUIC connection ID handling

Abstract

QUIC offers security and privacy for modern web traffic by closely integrating encryption into its transport functionality. In this process, it hides transport layer information often used for network monitoring, thus obsoleting traditional measurement concepts. To still enable passive RTT estimations, QUIC introduces a dedicated measurement bit - the spin bit. While simple in its design, tracking the spin bit at line-rate can become challenging for software-based solutions. Dedicated hardware trackers are also unsuitable as the spin bit is not invariant and can change in the future. Thus, this paper investigates whether P4-programmable hardware, such as the Intel Tofino, can effectively track the spin bit at line-rate. We find that the core functionality of the spin bit can be realized easily, and our prototype has an accuracy close to software-based trackers. Our prototype further protects against faulty measurements caused by reordering and prepares the data according to the needs of network operators, e.g., by classifying samples into pre-defined RTT classes. Still, distinct concepts in QUIC, such as its connection ID, are challenging with current hardware capabilities.